Optical modules are optical transceivers or optical transponders which integrate components for the purpose of transmission and reception of optical signals into a single packaged device. The integrated components generally serve to convert electrical signals to optical signals and optical signals to electrical signals. Optical modules are used in applications requiring digital optical transmission such as SONET/SDH, Gigabit Passive Optical Networks (GPONs), Ethernet Passive Optical Networks (EPONs), Ethernet, and Fibre Channel running across metro access networks, campus area networks, wide area networks, access networks, local area networks, and storage area networks.
As shown in FIG. 1, an optical module 110 comprises of: a laser or laser diode 102 that converts an electrical input signal into an optical output signal, an optical detector or photodiode (PD) 103 that converts an optical input signal into an electrical output signal, and high speed integrated circuits (IC) such as: a laser driver (LD) 104 that takes an input signal and generates an electrical signal that modulates the laser 102, a transimpedance amplifier (TIA) 106 that converts the current output of the optical detector 103 to a voltage as large as possible with a relative minimum of electrical noise, and a limiting amplifier (LA) 106 that converts the TIA output to a suitable electrical level for signal processing. Some high speed optical modules also incorporate serializer and deserializer (mux/demux) 108 functions as illustrated in optical module 112. A serializer multiplexes multiple parallel slow rate digital data streams into a single high speed digital stream and a deserializer demultiplexes a single high speed digital stream into multiple parallel slower rate digital streams. Serializers typically incorporate a clock multiplier unit (CMU) that converts a parallel input clock signal into a serial output clock signal and deserializers typically incorporate clock data recovery (CDR) functions that recover a clock signal from a serial analog data stream.
Manufacturers of optical networking systems find optical modules attractive, because the highly integrated packaging approach can cut several months of system development and manufacturing time, consume less power and increase port densities over board-level solutions built from discrete components. But with so much functionality in one module, timely and sufficient component supply becomes even more essential for successful system delivery. Multi-source agreement (MSA) developed so systems vendors can feel more confident about getting the components they need and being able to incorporate them without costly and time-consuming system redesigns. MSAs define specification for an optical module such as: physical dimensions or cage hardware, electrical connector interfaces, electrical levels, jitter, power supply, max power draw, EMI containment, optical connector interfaces, and thermal analysis.
Further with MSAs, system vendors can concentrate on system architecture and not optical research and development. However, this also limits the usefulness or utility of MSAs to solely be optical-to-electrical and electrical-to-optical conversion devices.
Examples of the MSA optical modules are shown in FIG. 2, such as small form factor pluggable (SFP) 210, 10G small form factor pluggable (XFP) 212 and XENPAK 214. An example of MSA optical modules used in a passive optical network (PON) is shown in FIG. 3. In a PON 300, an optical line terminal (OLT) 311 communicates with optical network units (ONUs) or optical network terminals (ONTs) 314 at or near customer premises 305 (e.g., residential homes, business, schools and government buildings) over optical fibers 306 and through optical splitters 310. OLT's 311 and ONUs/ONTs 314 can communicate by using MSA optical modules 302 (e.g., SFP) to generate optical signals. OLTs 311 are generally located at a Service Provider's Central Office 304 and communicate with Edge Routers 312.